A lubricant may be a liquid, a paste, or a solid with liquid lubricants being the most used. Lubricating oils may be used in automobile engines, transmissions, bearings, gears, industrial gears and other machinery to reduce friction and wear and to increase fuel economy. A number of components including, but not limited to dispersants, detergents, friction modifiers, antiwear agents, antioxidants, and anti-corrosion additives are typically present in fully formulated lubricating oils. For many lubricant applications, a viscosity index improver may also be included as a major component.
With the energy resources depleting and more stringent environmental regulations being adopted, there exists a greater demand to increase a fuel economy of vehicles and to decrease emissions in vehicle exhausts. Currently, organic friction modifiers are added to the lubricating oils to increase fuel economy. However, the level of the fuel economy achievable by organic friction modifiers is limited. Hence, there is a need for alternate methods for achieving improvements in fuel economy.
One method for increasing fuel economy is to provide lower viscosity grade lubricating oils. While providing lower viscosity lubricating oils may dramatically increase fuel economy, such lubricating oils may also increase wear. Wear may be partially reduced by using antiwear agents such as zinc dialkyldithiolphosphate (ZDTP). However, ZDDP contains phosphorus and its decomposition products may have deleterious effects on automotive catalyst systems for emission control. Accordingly, there remains an increasing need for methods for reducing friction and wear without adversely affecting emission control systems and without further depleting scarce natural resources.
With regard to the above, exemplary embodiments described herein provide a method for making a self-dispersing cerium oxide nanoparticles additive for lubricants, a lubricant composition containing the nanoparticles and a method for reducing boundary friction using the nanoparticles. The nanoparticles are made by reacting an organo-cerium salt, a fatty acid, and an amine in the substantial absence of water at a temperature ranging from about 150° to about 250° C. for a period of time sufficient to provide nanoparticles while injecting air into the reaction mixture during a portion of the reaction period. The reaction product includes from about 20 to about 40% by weight of the nanoparticles in a substantially organic medium.
In another embodiment, there is provided a method for reducing a friction coefficient adjacent a lubricated surface. The method includes providing an amount of reaction product comprising metal-containing nanoparticles dispersed in a fully formulated lubricant composition containing a base oil of lubricating viscosity, and applying the lubricant composition containing the metal-containing nanoparticles to a surface to be lubricated. The nanoparticles in the reaction product are self-dispersing and are a reaction product of reaction mixture of organo-cerium salt, fatty acid, and amine reacted in the absence of solvent at a temperature ranging from about 150° to about 250° C. for a period of time sufficient to provide nanoparticles. The reaction product includes from about 20 to about 40% by weight of the nanoparticles in a substantially organic medium.
Another embodiment of the disclosure provides a lubricant composition containing a base oil of lubricating viscosity and a boundary friction reducing amount of a reaction product containing metal-containing nanoparticles dispersed in the base oil. The nanoparticles are made by reacting an organo-cerium salt, a fatty acid, and an amine at a temperature ranging from about 150° to about 250° C. in the absence of solvent for a period of time sufficient to provide nanoparticles. The product of the reaction includes from about 20 to about 40% by weight of the nanoparticles in a substantially organic medium.
As set forth briefly above, embodiments of the disclosure provide a unique nanoparticle additive for lubricants and finished lubricant compositions containing the nanoparticle additive that may significantly improve the coefficient of friction of the lubricant composition and may reduce wear for relatively low viscosity lubricant compositions. An additive package containing the nanoparticle reaction product may be mixed with an oleaginous fluid that is applied to a surface between moving parts. In other applications, an additive package containing the metal-containing nanoparticle reaction product may be provided in a fully formulated lubricant composition.
The methods and compositions described herein may also be suitable for reducing emissions of CO and hydrocarbons (HC) from engines lubricated with the lubricant compositions described herein. It is well known that certain metals may be useful for improving the burning efficiency of fuels. For example, metal-containing nanoparticles from the lubricants may enter the combustion chamber by leaking around the piston rings thereby providing a catalytic source suitable for improving fuel combustion without directly adding metal compounds to the fuel. Other features and advantages of the methods described herein may be evident by reference to the following detailed description which is intended to exemplify aspects of the exemplary embodiments without intending to limit the embodiments described herein.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the embodiments disclosed and claimed. The phrases “having the formula” or “have the formula” are intended to be non-limiting with respect to nanoparticles or nanoalloy particles described herein. The formula is given for the purposes of simplification and is intended to represent mono-, di-, tri-, tetra-, and polymetallic nanoparticles.